That's true as a general maxim. But come on here. JK Rowling? One doesn't read Rowling for the beauty of her English or the originality of her characters or her deft exposition or her startling psychological insights. You read her for exactly the reason incandescens named- to find out what happens. If someone spoilers you for the book's action they remove the only reason I can think of to read Rowling.
What makes my eyes cross is that so far no-one seems to have said that. Indeed, people seem to read HP because they deeply love the paper-thin characters and because, as one of them said stunningly, 'I trust JK Rowling' to be an author worth reading. De gustibus indeed.
Myself I'm sorry she's become so popular. When I started her in 2001 her books were a light and pleasant diversion, prime summer reading. One read her as one reads mystery writers, to find out what happens, and very nice indeed. Now she's big business, one must read her the instant she comes out or else be told in half a dozen places who dunnit. Farewell minor pleasure, hello tedious chore.
Which is to say, I went to Book City this morning and said, sour, to the clerk, 'All we like sheep. The new Harry Potter?' He reached for a copy from the chair behind him: 'He's baa-a-a-ack.' I then went to the coffee shop and read Kamen Tantei Suzuki Tarou instead, just to make a point. But still. Read him I shall, interleaved with Gene Wolfe and kanji study to disperse the boredom, which so far is boring indeed.